In general, the lighter the load the higher the velocity usually is and will hit to a lower point of impact with the same sight picture. The reason for this is that lighter loads moving faster will exit the barrel before the muzzle has risen to its full elevation while in recoil mode.

While I do not own any Smith Revolvers produced after the mid 1990's I can say with certainty that the older and vintage models were built around and generally sighted in for 158 grain lead ammo and lighter and faster loads will shoot lower assuming one holds the same on the target.